Basic Wine Acid Testing Procedure

Achieving the correct acid content in winemaking is important to ensure Proper Fermentation, Keeping Qualities, Flavour, Character and Balance.

The proper time to determine and adjust acidity is in the fresh must prior to fermentation.

It is necessary to de-gas a fermenting must or new wine to achieve a correct acid reading as dissolved carbon dioxide has will affect the test results.

The acidity of a normal must is present in three forms: FREE ACIDITY, FIXED ACIDITY and VOLATILE ACIDITY.

The following procedure is designed to measure the TOTAL ACIDITY of the must. In North America the results are expressed in terms of PERCENTAGE OF TARTARIC ACID.

The following are general recommendations for the Total Acidity in finished wines:

Red Table Wines	0.60%
White Table Wines	0.70%
Sherries	0.50%
Dessert Wines	0.55%
Fruit Wines	0.60%

0.60 grams acid / 100 mL

Total Acid Test For White and Light-Coloured Wines

Be certain that all equipment is clean before use.
Draw a 15 cc sample of must or wine into the syringe and dispense into the clear plastic test beaker. Rinse syringe several times with water. Discard the rinse water.
Add 3 to 4 drops of the INDICATOR SOLUTION (Isopropyl Alcohol, Phenolphthalein) Swirl to mix.
Place beaker on a white sheet of paper in a well-lighted area.
Draw 10 cc’s of the Sodium Hydroxide Neutralizer Solution into the syringe. Slowly add the neutralizer 1 cc at a time, swirling the beaker after each addition until a slight pale pink colour change remains permanent throughout the entire sample in the beaker. (Pink colour streaks appear earlier but disappear upon swirling.)
This permanent colour change is known as the TITRATION END POINT. Further additions of the Sodium Hydroxide will deepen the pink colour but the test results will be erroneous.
If the initial 10 cc’s of Neutralizer Solution are insufficient to reach the END POINT, draw another 10 cc’s into the syringe and continue until the END POINT is reached.
Record the total number of cc’s of the Sodium Hydroxide Neutralizer solution required to reach the END POINT.
Each cc of Sodium Hydroxide Neutralizer solution required to reach the END POINT represents 0.1% total acidity read as tartaric. Example: if 7 cc’s of Sodium Hydroxide solution were required to reach the end point, the TOTAL ACIDITY of the must or wine would be 7 x 0.1% = 0.7%
Discard test sample and thoroughly rinse beaker and syringe with clear water
It is possible to titrate the TOTAL ACIDITY of the sample using a 1/10 N Sodium Hydroxide Solution. In this case each 2 cc’s of Sodium Hydroxide Neutralizer Solution required to reach the end point equals 0.1% total acidity.

Total Acid Test For Red Musts And Wines

Red musts and wines may be tested using the foregoing procedure. However, the END POINT is determined by a permanent slight grey or grey-purple colour rather than pink. Due to some difficulty in accurately observing the ITRATION END POINT the following procedure may alternatively be used.

Be certain that all equipment is clean before use.
Draw a 15 cc sample of must or wine into the syringe and dispense into the test beaker. Rinse syringe with water. Discard rinse water. Draw 15 cc’s of water (preferably distilled) into the syringe and add to the sample in the beaker
Add 3 to 4 drops of the INDICATOR SOLUTION (Isopropyl Alcohol, Phenolphthalein). Swirl to mix.
Proceed from step (4) of the foregoing test remembering that the END POINT will be indicated by a permanent grey or grey-purple colour rather than pink. Compute the Total Acidity of the sample in the same manner. The additional water added to the sample is only to make the titration end point more easily observed and does not affect the results.

Correcting Acidity

Increasing Acidity

The total acidity of low acid musts may be increased by the addition of ACID BLEND.
One level teaspoon (5ml) of ACID BLEND will increase the Total Acidity of 1 gallon by approximately 0.1%.
One ounce (28.4 g) of ACID BLEND will increase the Total Acidity of 5 gallons of must by approximately 0.15%

Approximate Amounts Of Acid Blend Per Gallon (4.5 L) Of Must To Raise Total Acidity To The 0.7% Level

% Acidity from Test	Level Teaspoons Acid Blend
0.10%	5 (25mL)
0.20%	4 (20mL)
0.30%	3 (15mL)
0.40%	2.5 (12.5mL)
0.50%	1.5 (7.5mL)
0.60%	0.75 (3.7mL)
0.70%	--

1oz. (28.4 g) Acid Blend = approximately 6 level teaspoons (30 mL)

Low-Acid Grape varieties may be blended with High-Acid Grape varieties to result in an acid balanced must. A common example of this is the blending of a low-acid California Vinifera variety with a high-acid Eastern Hybrid variety.

Lowering Acidity

The total acidity of a must may be reduced by the use of CALCIUM CARBONATE (Precipitated Chalk). One level teaspoon (5 mL) of Calcium Carbonate will lower the acidity of one gallon of must by approximately 0.1%. The total addition of calcium carbonate cannot exceed 2 level teaspoons (10 mL) per gallon or a chalky flavour may result in the finished wine.
Musts requiring a greater acid reduction than 0.2% should also be diluted with water. 1-1/2 cups (375 mL) of water will reduce the total acidity of one gallon of must by approximately 0.1%. It will be necessary to adjust the sugar content of the must after dilution.

Approximate Amounts Of Calcium Carbonate And/Or Water Per Gallon (4.5 L) To Lower Total Acidity To The 0.7% Level

% Acidity from Test	Level Teaspoons Calcium Carbonate	Water
0.70%	---	---
0.80%	1 (5mL)	---
0.90%	2 (10mL)	---
1.0%	2 (10mL)	1.5 cups (375mL)
1.1%	2 (10mL)	3 cups (750mL)
1.2%	2 (10mL)	5 cups (1.25L)

1 oz. Precipitated Chalk (28.4 g) = approximately 5 level teaspoons (30 mL)

High-Acid Grape varieties may be blended with Low-Acid Grape varieties to result in an acid balanced must. A common example of this is the blending of a high-acid Eastern Hybrid variety with a low acid California Vinifera variety. The type of blending may also be carried out with finished wines.
High-Acid musts may be blended with reconstituted Vinifera Grape Juice Concentrate which is often low in total acidity. This is a simple method of reducing the acidity while improving wine quality.
The total acidity of a finished wine may be reduced by sharply lowering the temperature for a period of time. In Northern areas the wine may be placed in a shed or unheated garage during the winter months. A four week period at temperatures around 25oF (-4oC) will cause a portion of the acid to precipitate in the form of potassium bitartrate.

NOTES: Store testing reagents tightly capped in a cool dark place to prevent deterioration. Keep reagents safely out of the reach of children.

< Previous Step | Next Step>